The invention relates to an instrument for screwing into the human skull an adapter which is intended to hold a pressure converter or a similar object, consisting of a pivot pin assembly with a screw grip which is connectible in a force-locking manner to the adapter.
In addition to cerebrospinal pressure measurement in the lateral ventricle via a catheter with an external pressure converter, methods for cerebral pressure measurement have succeeded in which commercial miniature pressure converters are implanted in the epidural skull cavity. In these methods it is important that the pressure sensitive membrane of the pressure receptor rests on the `dura mater` in a coplanar manner. An adapter which is screwable into the patient's skull to hold and position the pressure converter must be flush with the underside of the bone and must be sealed off from the environment. Adapters of this type are screwed into a prepared bore in the skull by means of an instrument. The instrument generally takes the form of a box spanner which can be connected to the adapter screw in a form and force locking manner by a transverse pin or a polygon profile at the proximal end. Since the thickness of the cranium bone can vary in different patients, the required screw-in depth of the adapter must generally be matched to the individual bone thickness. It is also desirable to control the screw-in depth, i.e. the distance of the proximal adapter surface from the underside of the bone, during the screwing-in operation.